Improved boron phosphate catalyst

ABSTRACT

Boron phosphate containing minor amounts of sulfate- and/or sodium-containing salts provides an improved dehydration catalyst for the synthesis of nitriles from carboxylic compounds or derivatives thereof and ammonia.

in 1mm: {states mm (151 3,674,708 Somich 1 July 4, 1972 [54] IMPROVEDBORUN PHOSPHATE [56] References Cited ATALY T C 8 UNITED STATES PATENTSh [72] T Lake Jackson Tex 2,668,175 2/1954 Reppe et a1 "260/4652 [73]Assignee: Monsanto Company, St. Louis, Mo. 3,121,733 2/1964 Von Schickhet al 260/4652 3,308,202 3/1967 De Gramont et a1. Flledi Dec-2,19703,342,820 9/1967 Brader ..252/432 x A l N .1 560 [21] pp 0 PrimaryExaminer-Patrick P. Garvin Related s Appncation Dam At!0rneyJohn W.Whisler, et a1,

[62] Division of Ser. No. 736,299, June 12, 1968, Pat. No. [57] ABSTRACTBoron phosphate containing minor amounts of sulfateand/orsodium-containing salts provides an improved dehydration [52] U.S.C1..252/432,B206O /4:5; catalyst for the Synthesis of "miles fromcarboxylic com 5 5L132 pounds or derivatives thereof and ammonia. 1e 0earc 5 Claims, N0 Drawings BACKGROUND OF THE INVENTION The presentinvention relates to an improved catalyst for use in synthesizingnitriles by the process comprising passing a vaporized mixture of acarboxylic compound and ammonia over a catalyst.

Nitriles are important intermediates for the synthesis of polyamides,e.g., polyhexamethylene adipamide (nylon 6,6), and their preparation hasbeen the subject of many investigations. In the synthesis of nitrilesfrom carboxylic compounds, e.g., carboxylic acids, and ammonia bypassing a vaporized mixture thereof over a suitable catalyst, manycompeting reactions are involved. One reaction leads to the formation ofnitrile; another to the formation of ketone. The ketone reaction isundesirable since the ketones must be separated from the nitrile andalso since ketones tend to undergo polymerization and decomposition atthe temperatures required for nitrile formation which results indeterioration of the catalyst.

Boron phosphate is known to be an effective catalyst in promotingnitrile formation. For example, in the continuous process forsynthesizing adiponitrile from adipic acid and ammonia at temperaturesranging from 300 550 C., adiponitrile is attained in high yields. Whenthe conversion of acid to nitrile falls below a level which results inan anhydrous and ammonia-free crude product containing less than 90-91percent adiponitrile, the useful life of the catalyst is usuallyconsidered to have lapsed.

The useful life of boron phosphate catalyst in the vapor phaseadiponitrile process is only about 70-80 pounds of adipic acidthroughput per pound of catalyst. When the useful life of the catalysthas lapsed, the catalyst is referred to as spent catalyst" and must beremoved from the process and replenished with fresh catalyst. Changingthe catalyst involves considerable man-hours, during which time theprocess must be shut down to effect the change. These factors coupledwith the cost per se of the catalyst contribute to the overall cost ofmanufacturing adiponitrile. A primary object of the present invention,therefore, is to increase the useful life of boron phosphate catalyst invapor phase nitrile synthesis processes and thereby reduce the cost ofpreparing the nitrile.

SUMMARY OF THE INVENTION The present invention provides an improvedcatalyst for use in synthesizing nitriles from a vaporized mixture of acarboxylic compound and ammonia, comprising boron phosphate containingat least one salt selected from sodiumand sulfate-containing salts inamounts sufficient to provide at least 0.009 percent and preferably from0.5-1 percent or more by weight of sodium, and at least 0.03 percent,and preferably from 005-0. 1 percent or more by weight of sulfate.

Boron phosphate is conventionally prepared by reacting a slight molarexcess of phosphoric acid with boric acid in the cold, and isolating andbaking the product at about 350 C. until a hard mass is formed asdescribed in U.S. Pat. No. 2,200,734 issued to Arnold and Lazier. Thecatalyst of the present invention, referred to herein as modified boronphosphate, may be prepared by adding a sodiumand/or sulfate-containingsalt to boric acid and then reacting the saltcontaining boric acid withphosphoric acid in the manner described in U.S. Pat. No. 2,200,734.

Suitable sodium and sulfate-containing salts, although not limitedthereto, include, for example, alkali and alkaline earth metal sulfatesand sodium salts of inorganic acids, e.g., sodium phosphate, chloride,borate, etc. Any sodium or sulfate salt may be used to provide themodified boron phosphate which does not adversely affect formation ofthe nitrile, e.g., the purity or yield thereof. Preferred salts aresodium sulfate and sodium borates, e.g., sodium tetraboratepolyhydrates.

Preparation of nitriles by reacting nitrile-producing materials andammonia in the presence of a suitable catalyst at elevated temperaturesis well known in the prior art and, therefore, is not discussed indetail herein. Prior art relating to nitrile synthesis of this typeinclude U.S. Pat. Nos. 2,200,734; 2,377,795; 2,646,344; 3,282,859; and3,324,165.

PREFERRED EMBODIMENT OF THE INVENTION CATALYST PREPARATION Sodiumtetraborate pentahydrate (30 lbs.) and 0.83 lbs. of anhydrous sodiumsulfate were added to 400 lbs. of boric acid. The combined materialswere added to 880 lbs. of 87 percent phosphoric acid and mixed for 30minutes. The resulting paste was dried at 150 C. for 18 hours, ignitedat 350 C. for 7 hours, and granulated and screened. Normally, the boronphosphate catalyst is prepared using 400 lbs. of boric acid and 817 lbs.of phosphoric acid, processed in the same manner.

ADIPONITRILE PREPARATION The modified boron phosphate catalyst preparedabove was charged to a multitube tube and shell converter and a mixtureof vaporized adipic acid and ammonia at a 1:1 weight ratio was passedover the catalyst at a uniform rate. The feed mixture temperature was450 C. and hot flue gas was circulated through the converter shell tomaintain a catalyst bed temperature of about 370 C. The product wascondensed to form an aqueous crude adiponitrile solution and someadiponitrile mist which was scrubbed with crude adiponitrile. At thispoint ammonia was removed as an off-gas and the adiponitrile wascollected, purified sequentially by distillation, chemical purification,caustic treatment, washing and further distillation. The conversion,based on adiponitrile content of the anhydrous ammonia-free crudeproduct, was 93.40 percent. The useful life of the modified catalyst was116 pounds of adipic acid throughput per pound of catalyst. At thispoint the adiponitrile content in the anhydrous and ammonia-free crudeproduct had dropped below 93 percent. The conversion level wasdetermined by continuous sampling and analysis of the crude product.

The useful life of normal boron phosphate catalyst was determined by theabove procedure using identical amounts of catalyst and reactants andfound to be about 77 pounds of adipic acid per pound of catalyst.

Comparison of Modified Catalyst to Normal Catalyst Re Conversion LevelsTwelve runs were made according to the above adiponitrile preparationprocedure to determine the useful catalyst life for modified boronphosphate catalyst and for normal boron phosphate catalyst; the averageconversion, expressed as percent adiponitrile in the anhydrous andammonia-free crude product was also determined. Six runs were made witheach catalyst under as nearly identical conditions as possible. Theresults of these determinations are given in Table 1.

TABLE 1 Modified Catalyst Normal Catalyst Throughput, Lbs. Con-Throughput, Lbs. Con- Adipic Acid/Lb. version, Adipic Acid/Lb. version,Run Catalyst Catalyst l 92 94.07 2 77 94.41 3 84 94.30 4 7l 93.69 5 9594.34 6 66 93.18 7 93.75 8 63 94.32 9 I 15 93.49 IO 71 94.56 I l I0594.16 l2 7l 93.86

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The results shown in Table 1 clearly indicate that the modified boronphosphate of the present invention provides an improved catalyst for thesynthesis of adiponitrile from adipic acid and ammonia. The throughputsfrom the modified catalyst were significantly better than that from thenormal boron phosphate catalyst and provided substantially the sameconversion. The increase in adipic acid throughput permits fewercatalyst changes, thereby reducing the man-hours required in themaintenance of the synthesis.

The addition of even trace amounts of either sulfate or sodium salts toboron phosphate results in a measurable improvement in the function ofthe catalyst in nitrile synthesis. Best results are attained, however,when the boron phosphate catalyst contains from 0.03-5 percent on weightof sulfate and/or from 0.009-5 percent on weight of sodium; greaterquantities can be added to boron phosphate, but at concentrationsgreater than about 5 percent no significant increase in catalyst life isobserved. Instead of preparing the modified boron phosphate by addingthe salts to the boric acid prior to reacting it with the phosphoricacid, alternately the salts may be added to the phosphoric acid or themodified boron phosphate may be prepared by any other means wherebysulfate and/or sodium-containing boron phosphate is attained.

Thus far, owing to the commercial importance of adiponitrile, themodified catalyst has been used primarily to promote adiponitrileformation in the conventional vapor phase reaction of ammonia withadipic acid. However, the modified catalyst may be used in any way ormanner in which normal boron phosphate may be used, for example, toprepare other nitriles by the vapor phase reaction of any monobasic acidor other dibasic acid (or their amide or ammonium salts) with ammonia.Thus, the modified catalyst may be used in the preparation of saturatedor unsaturated mononitriles or dinitriles from Q to C monoor dibasicfatty acids, or in the preparation ofortho-phthalonitrile from phthalicacid.

What is claimed is:

l. A dehydration catalyst consisting essentially of boron phosphate andat least one salt selected from the group consisting of sodium andsulfate salts, said sodium salt being a salt of an inorganic acid in theamount of 0.009 to 5 percerit by weight and said sulfate salt being analkali or alkaline earth metal sulfate in the amount of 0.03-5 percentby weight.

2. The catalyst of claim 1 wherein the salt is selected from the groupconsisting of sodium sulfate and sodium borates.

3. The catalyst of claim 1 wherein the catalyst contains a sodium saltand sulfate salt.

4. The catalyst of claim 2 wherein the sodium borate is sodiumtetraborate pentahydrate.

5. The catalyst of claim 3 wherein the sodium salt is sodium tetraboratepentahydrate and the sulfate salt is sodium sulfate.

2. The catalyst of claim 1 wherein the salt is selected from the groupconsisting of sodium sulfate and sodium borates.
 3. The catalyst ofclaim 1 wherein the catalyst contains a sodium salt and sulfate salt. 4.The catalyst of claim 2 wherein the sodium borate is sodium tetraboratepentahydrate.
 5. The catalyst of claim 3 wherein the sodium salt issodium tetraborate pentahydrate and the sulfate salt is sodium sulfate.